Few technological innovations have revolutionized technology as much as integrated circuits. Since the advent of integrated circuits, professional and consumer electronic products have become more sophisticated and smaller. As is known, integrated circuits allow complex circuitry to be implemented in extremely small packages. For example, such revolutionary integrated circuits include the microprocessor, video graphics circuits, audio Codec, memory, etc.
As integrated circuit technology continues to evolve, integrated circuit manufacturers are producing customized integrated circuits for particular clients. In many cases, the customized integrated circuit is similar to standard products with some customization for the particular client. For customized integrated circuits, the IC manufacturer typically includes identifying circuitry deposited on the die to identify the customized device. Such identifying circuitry typically is coupled to an exterior bonding pad of the die which in turn is coupled to a pin of the integrated circuit package. As such, when the integrated circuit is tested, a signal is applied to the testing pin, which is subsequently provided to the identifying circuitry on the die. If the signal is processed properly, the integrated circuit is identified as the customized integrated circuit. Such identifying circuitry may be as simple as a resistor having a known current applied across it, where the voltage is measured to identify the circuit. Alternatively, the identifying circuitry may be a register or a plurality of registers that store identifying bits wherein the bits are read from the registers via the package pin.
While such identifying circuitry works well to identify integrated circuits, they do require at least one package pin to be dedicated for the testing circuitry. As commercial demands are pushing integrated circuit manufacturers to make smaller integrated circuits in smaller packages, package pins are at a premium. As such, it is difficult if not impractical to dedicate a pin or pins to an integrated circuit identifying circuitry.
Therefore a need exists for a method and apparatus that utilize existing pins for identifying customized integrated circuits.